He's right. I work in a call center (not calling on the phones, I keep up the infrastructure) where we do mostly market research for our clients which involves calling their customers. Utility companies, medical offices, consulting services, they will all honor do-not-call requests and so will any legitimate call center business.
That is thankless work, the people on the phones are mostly not scum, but the number of people that answer the phone and treat them as such makes me feel for them so I'm happy to look the other way at some minor bad behavior like being short with a person or hanging up, when every third person they talk to is some jerk who only knows how to yell "IM ON THE DO-NOT-CALL LIST I JUST TALKED TO YOU LAST WEEK I ALREADY TOLD YOU NOW WHAT YOU ARE DOING IS ILLEGAL GIVE ME YOUR MANAGER RIGHT NAO!!1one" Just because you talked to _some_ call center somewhere, it does not follow that every call center in the fleet automatically knows you are not to be contacted.
We have do-not-call lists, and the best way to make sure you get that treatment is to ask for it. You don't have to ruin your day and someone else's by getting mad about it. Five magic words can liberate you: "do not call me again".
Second best way: when you sign up for services, don't give them your phone number! They can't give it to us if they don't have it to begin with. If hearing the phone ring makes you so mad, seriously just don't give it out to any companies that could just as easily deal with you by post.